An overall system of bones, teeth, temporomandibular joints, and muscles is considered in functional dentistry. Complicated movement sequences of the whole system, which are individual to the patient, are increasingly recorded by means of electronic methods that are able to register the position of the lower jaw in relation to the upper jaw at different times in six degrees of freedom (three rotations, three translations). Such movement records may be available as condylography data.
DE 10 2004 002 953 A1 describes a method in which the relative motions of the jaws are measured on the basis of two ultrasonic transducers and sensors rigidly connected to the upper and lower jaw. By means of a prepared representation of the thus obtained condylography data, the dentist is able, for example, to also depict the movement trajectory of an imagined hinge axis of the temporomandibular joints during masticating. This prepared representation of the movement trajectory of an imagined hinge axis corresponds to the measurement that is recorded, usually by direct mechanical means, in relatively old measurement systems (so-called axiography systems). Such axiography systems do not measure the full six degrees of freedom of the lower jaw position, but only an angle/path combination from which the spatial position of the lower jaw in relation to the upper jaw usually cannot be uniquely established. The axis tracing is nevertheless often displayed, even in the case of condylography systems with the full six degrees of freedom, because medical practitioners are trained to diagnose pathologies on the basis of this tracing data.
Even if many pathologies in the joint and muscular anatomy can be diagnosed by condylographies or axiographies, the diagnosis often needs to be differentiated by means of imaging methods which depict hidden anatomy in a geometrically correct manner. Examples for such imaging methods include cone-beam computed tomography (CBCT), magnetic resonance imaging (MRI), and computed tomography (CT). Making tomographic images is often also essential for the therapy planning that follows the diagnosis. This is particularly the case if changes have to be undertaken on the bone, e.g., during an orthodontic treatment or in a surgical intervention.
The positional relationships between the jaws were until now typically not even scanned during a tomographic scan. The patient is instead scanned with an undefined jaw position by virtue of said patient being fixed with a generic bite block or by virtue of his head resting on a chin support. If a bite block is used, the teeth are slightly opened; in the case of the chin support, the teeth are in occlusion or maximum intercuspation.
Some recording protocols, in particular, in magnetic resonance imaging, prescribe a specific jaw opening for being able to diagnose the position of the disk in the temporomandibular joint. This jaw opening is typically established by a cylinder with a diameter of a few centimeters which the patient holds between his teeth during the recording. Opening the patient's mouth by means of a cylinder, however, only permits very approximate influencing of the relation between upper and lower jaw. This can moreover only set relations in which the temporomandibular joints are in a central position. Transverse and lever forces cannot be exerted by a cylinder.
This is aggravated by the fact that patients are often referred from an orthodontist or dentist to a specialist in recording tomographic volume data who, however, generally does not have specialist knowledge in the field of dentistry. Such specialists are generally unable to monitor or set the precise position of the jaw.
When diagnosing and treating problems of the temporomandibular joint, care should be taken, in principle in all recordings of the jaws, that, where possible, no unnatural or undesired forces act on the jaws. By way of example, when performing a tomographic method in the intercuspation position (ICP), there may be an—albeit small—deformation of the jaws, or the temporomandibular joint may assume an unnatural position due to the muscle power. This would naturally significantly reduce the quality of the digital images. Tomographic recordings, and other recordings, which were recorded in the ICP are, as a matter of principle, furthermore relatively unsuitable since the image data in the boundary regions between upper and lower jaw can often only be assigned poorly to the respective jaw in an automated manner.
An aspect of the present invention is to make further use of the diagnostic options emerging from condylography.
In an embodiment, the present invention provides a method for generating a virtual jaw image depicting a digital lower jaw image in relation to a digital upper jaw image in different positions which includes performing a movement recording method to obtain a movement record. The movement recording method comprises producing at least one position data record over a defined time. Each of the at least one position data record describes a spatial position of a lower jaw in relation to an upper jaw at a specific time. Surface sections of the upper jaw and of the lower jaw are scanned at the defined time during the movement recording method so as to obtain a spatial relation of the surface sections during the defined time. Digital upper jaw images and digital lower jaw images are recorded. At least one of the at least one position data record of a virtual position of the digital lower jaw image is assigned in relation to the digital upper jaw image. One of the at least one position data record is selected so as to obtain a selected position data record. The digital lower jaw image is virtually aligned in relation to the digital upper jaw image in accordance with the selected position data record so as to produce the virtual jaw image. The virtually aligning corresponds to a real position of the lower jaw in relation to the upper jaw in accordance with the selected position data record.